Cochlear implant electrode and method of making same

ABSTRACT

A cochlear stimulation lead having a pre-curved electrode array is provided. The molding process provides memory to the curved part of the lead. The lead may be made having a stylet insertion channel that extends from a slightly curved or substantially straight section and into the highly curved section of the lead. Because high compliance is desired for the lead in cochlear stimulation applications, the compliance is controlled not only by the taper at the distal end of the lead and overall lead thickness, but also by choosing the material hardness of the lead carrier/covering and employing compliant zigzagged conductor wire. In addition, differential lead compliance/stiffness can be achieved by using a stiff tubing that forms part of the stylet insertion channel.

[0001] The present application claims the benefit of U.S. ProvisionalPatent Application Serial No. 60/412,253, filed 19 Sep. 2002, whichapplication is herein incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to implantable stimulation devices,and, more particularly, to electrode arrays for stimulation of thecochlea. Electrode arrays consist of electrode contacts generally placedalong one side of an elongate carrier so that when the array isimplanted within one of the cochlear ducts such as the scala tympani,the electrode contacts are positioned in close proximity to the cellsthat are to be stimulated, allowing such cells to be stimulated withminimal power consumption.

[0003] For purposes of clarity, as used herein, an implantablestimulating lead is a device that has one or more electrode contactsthat deliver current to tissue to be stimulated. An electrode contact isthat part of the stimulating device which is actually electricallyconductive and is in contact with the body tissue that is to bestimulated. The term “electrode” may sometimes be used narrowly as theelectrode contact or contacts only and, other times, more broadly, asthe electrode contact or contacts and all the surrounding structure,including the insulation carrier that the contacts are placed upon, aswell as the conductor wires and any other assemblies within or on theinsulation carrier. As used herein, the broad definition of the term“electrode” will be adopted, which includes the electrode contacts andall surrounding structures. In addition, when the term “lead” is used,it will be used interchangeably with the broad use of the term“electrode.” The term “electrode array” will refer to that portion ofthe electrode or lead that includes all of the electrode contacts andthe immediate structures upon which the electrode contacts are attached.Thus, the term “electrode array” may be narrower than the broad term“electrode” in that any carrier insulation and conductor wire that isnot immediate to the electrode contacts will not be included in the term“electrode array.”

[0004] Hearing loss, which may be due to many different causes, isgenerally of two types: conductive and sensorineural. Of these,conductive hearing loss occurs where the normal mechanical pathways forsound to reach the hair cells in the cochlea are impeded, for example,from damage to the ossicles. Conductive hearing loss may often be helpedby using conventional hearing aids that amplify sounds so that acousticinformation can reach the cochlea and the hair cells. Some types ofconductive hearing loss are also amenable to alleviation by surgicalprocedures.

[0005] In many people who are profoundly deaf, however, the reason fortheir deafness is sensorineural hearing loss. This type of hearing losscan arise from the absence or the destruction of the hair cells in thecochlea which transduce acoustic signals into auditory nerve impulses.Individuals with sensorineural hearing loss are unable to derive anybenefit from conventional hearing aid systems no matter how loud theacoustic stimulus is, because the mechanism for transducing sound energyinto auditory nerve impulses has been damaged. Thus, in the absence ofproperly functioning hair cells, auditory nerve impulses cannot begenerated directly from sounds.

[0006] To overcome sensorineural deafness, cochlear implant systems orcochlear prostheses have been developed, which can bypass the hair cellslocated in the vicinity of the radially outer wall of the cochlea bypresenting electrical stimulation to the auditory nerve fibers directly.This leads to the perception of sound in the brain and provides at leastpartial restoration of hearing function. Thus, most of these cochlearprosthesis systems treat sensorineural deficit by stimulating theganglion cells in the cochlear directly using an implanted electrode aor lead that has an electrode array.

[0007] A cochlear prosthesis operates by directly stimulating theauditory nerve cells, bypassing the defective cochlear hair cells thatnormally transduce acoustic energy into electrical activity to theconnected auditory nerve cells. In addition to stimulating the nervecells, the electronic circuitry and the electrode array of the cochlearprosthesis separate the acoustic signal into a number of parallelchannels of information, each representing a narrow band of frequencieswithin the perceived audio spectrum. Ideally, each channel ofinformation should be conveyed selectively to a subset of auditory nervecells that normally transmits information about that frequency band tothe brain. Those nerve cells are arranged in an orderly tonotopicsequence, from the highest frequencies at the basal end of the cochlearspiral to progressively lower frequencies towards the apex. In practice,however, this goal can be difficult to realize because of the particularanatomy of the cochlea.

[0008] Over the past several years, a consensus has generally emergedthat the scala tympani, one of the three parallel ducts that make up thespiral-shaped cochlea, provides the best location for implantation of anelectrode array used as part of a cochlear prosthesis. The electrodearray to be implanted in the scala tympani typically can consists of athin, elongated, flexible carrier containing several longitudinallydisposed and separately connected stimulating electrode contacts,conventionally numbering about 6 to 30. Such an electrode array ispushed into the scala tympani duct in the cochlea to a depth of about20-30 mm via a surgical opening made in the round window at the basalend of the duct.

[0009] In use, the cochlear electrode array delivers electrical currentinto the fluids and tissues immediately surrounding the individualelectrode contacts to create transient potential gradients that, ifsufficiently strong, cause the nearby auditory nerve fibers to generateaction potentials. The auditory nerve fibers branch from cell bodieslocated in the spiral ganglion which lies in the bone or modiolus,adjacent to the inside wall of the scala tympani. Because the density ofelectrical current flowing through volume conductors such as tissues andfluids tends to be highest near the electrode contact that is the sourceof such current stimulation at one contact site tends to selectivelyactivate those spiral ganglion cells and their auditory nerve fibersthat are closest to that contact site. Thus, it is important generallyfor the electrode contacts to be positioned as close to the ganglioncells as possible. Conventionally, after implant, the electrode arrayconsisting of electrode contacts should hug the modiolar wall (or insidewall of the scala tympani). When the electrode side of the array ispositioned closest to the modiolar wall, the electrode contacts are onthe medial side of the lead.

[0010] In order to address the above need, it is known in the art tomake an intracochlear electrode array that includes a spiral-shaped,resilient carrier which generally has a natural, spiral shape so thatthe array better conforms to the shape of the scala tympani. See, e.g.,U.S. Pat. No. 4,819,647, which is incorporated herein by reference.While the electrode array with a spiral-shaped carrier shown in the '647patent represents a significant advance in the art, it lacks sufficientshape memory to allow it to return to its original curvature (oncehaving been straightened for initial insertion) and to providesufficient hugging force to wrap snugly against the modiolus of thecochlea.

[0011] It is also known in the art, as shown in U.S. Pat. Nos. 5,545,219and 5,645,585, to construct an electrode carrier from two initiallystraight members, a rod-like electrode carrier and a flexible rod-likepositioning member. The '219 and '585 U.S. patents are also incorporatedherein by reference. As shown in these patents, the two members extendin substantially parallel relation to and closely alongside each other,but are connected to each other only at their respective leading andtrailing ends. After implant, a pushing force is applied to thepositioning member so that it is forced to assume an outwardly archedconfiguration relative to the electrode carrier, thereby forcing theelectrode carrier into a close hugging engagement with the modiolus andplacing the electrode contacts as close to the cells of the spiralganglion as possible. The '219 patent, in particular, shows in FIGS.1-10 and describes in the accompanying text an excellent summary ofprior art electrodes and the deficiencies associated therewith. Otherpatents relevant to the subject matter of cochlear stimulation leadsare: U.S. Pat. Nos.: 6,125,302; 6,070,105; 6,038,484; 6,144,883; and6,119,044, which are all herein incorporated by reference.

[0012] While the electrode arrays taught in the above-referenced '219and '585 patents are based on the correct goal, i.e., to force theelectrode carrier into a close hugging engagement with the modiolus, itdoes so only by using an additional element that makes manufacture ofthe lead more difficult and expensive and only by applying an additionalpushing force to an electrode structure after it has already beeninserted into the cochlea. Such additional pushing force may causedamage to the delicate scala tympani or cause the electrode contacts totwist or to separate away from the modiolus, rather than be placed inthe desired hugging relationship.

[0013] Thus, while it has long been known that an enhanced performanceof a cochlear electrode or lead can be achieved by proper placement ofthe electrode contacts close to the modiolar wall of the cochlea, amajor challenge has been obtaining a electrode/lead design that does notuse excessive force to achieve this close placement. There has eitherbeen the need for application of an external and possibly unsafe forceor a lack of sufficient shape memory to allow the electrode to assume orreturn to the desired curvature (after the electrode has been initiallystraightened during insertion) so that the electrode array wraps snuglyaround the modiolus of the cochlea.

[0014] It is thus evident that improvements are still needed to obtain acochlear electrode that has shape memory, is easily implanted so thatexcessive force is not required, and can be easily manufactured.

SUMMARY OF THE INVENTION

[0015] The present invention addresses the above and other needs byproviding a cochlear electrode design having a curved electrode arrayfor insertion into a cochlear cavity and methods for manufacturingvarious aspects of the cochlear electrode of the present invention.

[0016] In one aspect of the invention, there is provided an improvedstimulation lead for implanting into a body cavity. The lead comprises:a flexible carrier having a proximal end, a distal end, a medial sideand a lateral side; a distal, pre-curved lead section having memory; aplurality of electrode contacts embedded at the distal end of the lead,which electrode contacts comprise an electrode array; a plurality ofconductor wires embedded in the carrier, each conductor wire connectedto at least one electrode contact; and a longitudinal, stylet insertionchannel within the carrier extending into at least a part of the distal,pre-curved lead section.

[0017] The pre-curved section of the lead, which includes at least someof the electrode array, has memory because the electrode contacts andconnected conductor wires which form an electrode contact assembly arepre-bent into the desired curvature before the flexible carrier isformed around the electrode contact assembly. Thus, not only is thecarrier molded into a predetermined curved shape having memory, but theelectrode contact assembly is also pre-bent into a desired curvature tocooperate with the molded carrier shape. The pre-curved lead section hasan internal, elastic characteristic, whereby straightening the curvedsection exerts an elastic, contractive tension, tending to restore thatsection to its initial shape.

[0018] The present invention utilizes various components in the leaddesign to cooperate and to achieve a desired, high compliance in thecurve section of the lead. Specifically, conventional conductor wiresare typically straight wires or coiled wires. The conductor wires ofchoice, however, are zigzag wires because they are relatively compliant,offer fracture resistance to bending and can be compactly bundled. Whilestraight wires can be compactly bundled, they are more susceptible tobending fractures than zigzag or coiled wires. Coil wires are not aseasily bundled compactly as straight or zigzag conductor wires. Althoughzigzagged conductor wires are preferably used, it is emphasized that thelead design of the present invention can incorporate a variety ofconductor wire configurations including straight and coil type wires.

[0019] The lead of the present invention includes a stylet insertionchannel which is used during implantation of the lead to help guide thelead into a cavity. For example, in the case of a cochlear stimulatinglead, an insertion stylet may be inserted into the insertion channel tofacilitate the initial placement of the lead tip into the scala tympani.While the stylet insertion channel may be directly formed within thelead carrier itself, such a stylet insertion channel may not giveoptimal results because the compliant carrier material may have asurface texture that is too sticky to function well as a stylet channelwall. Accordingly, the lead of the present invention not only includes astylet insertion channel, but a part of this channel may be made from athin-wall tubing that is a different material than the carrier material.A particularly suitable tubing material is Teflon® orpolytetrafluoroethylene (PTFE) polymer.

[0020] Use of a Teflon tubing in the lead serves two major purposes.First, the Teflon is much stiffer than carrier material which isgenerally silicone or polyurethane. Incorporating a Teflon tubingtherefore provides added stiffness to that part of the lead. Second, theTeflon tubing makes inserting and withdrawing a stylet into and out ofthe stylet insertion channel much easier because Teflon is a hardermaterial and exhibits less friction than silicone or polyurethane. As aconsequence, Teflon also does not tear as easily as the carriermaterial.

[0021] As yet another embodiment of the lead of the present invention,an overmold can be attached over the opening of the stylet insertionchannel to minimize fluid and bacteria from entering the styletinsertion channel. The overmold may be made from the same material asthe lead carrier material, e.g., silicone or polyurethane. A slit in theovermold is placed to allow passage of the insertion stylet through theslit and into the stylet insertion channel. The slit must be sized andconfigured to permit the stylet to pass easily through the slit. Afterthe stylet is withdrawn, the slit, being made of a compliant material,will self-seal to some extent, as it returns to its originalconformation.

[0022] As a further embodiment of the stimulation lead of the presentinvention, the use of the slit may not always be sufficiently tight tokeep out fluid and bacteria and hence two additional devices may be usedfor sealing the slit in the overmold. The first device is a pin plugthat has a head and a tail pin, which tail pin may have a curvature. Thepin plug may be inserted head first into the slit in the overmold toseal the slit through a compression/friction fit. After the head hasbeen inserted into the slit, the tail pin may be left outside theovermold. A second device is a malleable ring that may be formed intothe overmold and encircles the slit. After the lead has been implantedwith the insertion stylet and the stylet withdrawn, the ring may becrushed around the slit to provide a compression seal.

[0023] The lead, in accordance with the present invention, can be madein at least two specific embodiments for cochlear stimulation. One leadcan be made for medial placement in the human scala tympani, which isone duct in the cochlea. This embodiment of the lead has a pre-curvedsection that is spiral shaped. The distal curved part of this lead has alength, taper, and curvature such that after implantation, the electrodearray is implanted approximately one spiral turn in the scala tympaniduct. This lead also can include a stylet insertion channel that extendsinto the distal curved section of the lead and also part of the slightlycurved (substantially straight) lead section. The stylet insertionchannel can be partly comprised of a Teflon tubing. It is emphasizedthat the tubing specifically does not extend into the aggressivelycurved, distal part of the lead, because if that were so, this curvedpart would become unacceptably stiff and non-compliant. It is alsoemphasized that the stylet channel continues into the distal curvedsection of the lead, but this section of the channel is formed from thecarrier material itself. The Teflon tubing forms only that part of thestylet insertion channel that is the substantially straight or slightlycurved section of the lead where additional stiffness is desired. Thus,use of the Teflon tubing contributes advantageously to a lead havingdifferential compliance along its length.

[0024] Another, second embodiment of the cochlear lead is suited fordeep, lateral (outer) wall placement in the scala tympani. With thisembodiment, the distal section of the lead is hooked shape. This hooked,curved portion is comparatively longer than the lead embodiment formedial placement, in order to allow the second lead embodiment to beimplanted into the scala tympani between about 1 to 2 turns. Because ofthe hook shape, when the second embodiment of the lead is implanted, thelateral side of the lead contacts the lateral or outer wall of the scalatympani. Such lateral contact may facilitate the deeper, up to 2 turn,implantation of the electrode array.

[0025] As an additional feature of the second cochlear lead embodiment,the very tip of the tapered, curved hook may be constructed to be“super-flexible.” The super-flexible tip is short enough such that onlya subset of the electrode contacts are actually part of thissuper-flexible tip. The super-flexible tip is achieved by (a) making thethickness of the tip very thin relative to the other part of the curvedhook and (b) by excluding any part of the stylet insertion channelwithin this tip, since including a channel would necessarily require toothick a carrier and prevent super-flexibility. The super-flexible tippermits the lead to easily conform to the curvature of the scala tympanias the lead tip is being inserted and also to apply light pressure tothe lateral wall of the scala tympani in order to minimize injury to thewall during insertion of the electrode array.

[0026] In another aspect of the invention, a method of manufacturing astimulating lead having a pre-curved tip is provided. This methodcomprises: (a) attaching a plurality of inert electrode contacts onto achemically dissolvable strip substrate having a first, distal end and asecond, proximal end; (b) coupling each electrode contact to a conductorwire to create an electrode array assembly; (c) attaching the first,distal end of substrate to a revolving dowel, which dowel is integratedinto a mold and inside a cavity; (d) attaching the proximal, second endof the substrate to a restraint which applies tension to the electrodearray assembly; (e) turning the dowel to create a predeterminedcurvature on the distal end of the electrode array assembly; (f)delivering a body-compatible carrier material into the cavity and aroundthe electrode array assembly to create a carrier/covering; (g) releasingthe formed lead from the mold; and (h) applying a weak acid and heat tothe chemically active substrate to dissolve away the substrate andexpose the inert, electrode contact on the surface of the lead. Themethod described can produce a lead with an electrode array having acurved tip with elastic, memory properties.

[0027] The process above may be modified to incorporate a styletinsertion channel in the body of the lead. This is accomplished byinserting between step (e) and (f), the step (e1): placing a mandrelinto the cavity, oriented approximately parallel to the electrode arrayassembly, wherein the proximal end of the mandrel is situated to escapecoverage by injected carrier material. Further, anytime after step (g),another step is added: (g1) pulling the mandrel out of the carrier tocreate a stylet insertion channel with a channel opening on the lead. Inaddition, after the mandrel is pulled out, the opening of the channelopening may be covered with an overmold having a slit openingtherethrough to allow access into the stylet channel. This process canbe used to produce a pre-curved lead having a stylet channelconcurrently in the portion of the substantially straight or slightlycurved section of the lead as well as the aggressively curved section ofthe lead.

[0028] As an alternative embodiment of the above method, the styletchannel may include a thin-wall Teflon tubing. This is accomplished byinserting between step (e) and (f) the steps: (e1) placing a mandrelinside the lumen of a thin-walled Teflon tubing; and (e2) placing thecombination of the Teflon tubing with the inserted mandrel inside thetubing into the mold cavity, the combination oriented approximatelyparallel to the electrode array assembly, wherein the proximal end ofthe mandrel is situated to escape coverage by the delivered carriermaterial. Also any time after step (g), the following step can takeplace: (g1) pulling the mandrel out of the Teflon tubing to create thestylet insertion channel. While the mandrel may be made from variousmaterials, one option is to use a mandrel that is made of Teflon. Afterthe Teflon mandrel has been pulled out of the formed lead, leaving theTeflon tube incorporated into the lead, an overmold, which has a slitopening, may be attached over the opening of the stylet insertionchannel. This latter embodiment produces a differentially compliantpre-curved lead by employing the Teflon® tubing as a stiffener.

[0029] The above-described manufacturing process can produce apre-curved lead having a stylet channel extending from the curved,distal end to the substantially straight section of the lead. Again, itis emphasized that the Teflon tube comprises only a part of the totallength of the stylet insertion channel. That is, the tube occupies onlythe substantially straight or slightly curved lead section and not thedistal, aggressively curved section.

[0030] The presence of the Teflon tubing is advantageous as it presentsless friction and is more resistant to tears than the carrier materialwhich is often silicone or polyurethane. An insertion stylet can be moreeasily inserted into and withdrawn from the Teflon tubing with thereduced possibility of a wall tear in the channel. A second importantbenefit provided by the Teflon tubing is that it provides differentialstiffness to the lead. The distal, tapered, curved portion of the leadcan be compliant and gentle while being inserted into the scala tympani,while the substantially straight section of the lead is made stiffer bythe presence of the Teflon and thereby facilitates the directionalplacement of the lead near the target cochlea.

[0031] In another aspect of the present invention, a method is providedfor implanting a stimulating electrode having an insertion styletchannel with a channel opening on the lead body. The method comprises:(a) implanting the lead using the stylet; (b) withdrawing the styletfrom the lead; and (c) capping the insertion stylet channel opening. Asdescribed, the channel opening may be capped by attaching an overmoldwith a slit that is sized to permit through access for an insertionstylet. The slit may be subsequently sealed with a pin plug or with amalleable ring encircling the slit.

[0032] As yet another aspect of the present invention, a lead system isdescribed comprising: a cochlear lead, a pin plug, and an insertiontool. The cochlear lead includes: a flexible carrier having a proximalend and a distal end; a stylet insertion channel incorporated into theflexible carrier; and an electrode array placed on the distal lead end.The pin plug for capping the insertion stylet has a head and tail pinwith a curvature in the tail pin. The insertion tool has a first end andsecond end. The first end of the insertion tool has a pin plug holdingchannel that accommodates and holds the tail pin with a friction fit tohelp insert the head of the pin plug into the lead to cap the styletinsertion channel.

[0033] It is thus a feature of the present invention to provide a leaddesign having a pre-curved electrode array having an elasticcharacteristic which tends to restore the electrode array to itspre-curved shape after implantation.

[0034] It is another feature of the invention to provide specificembodiments of the lead which have compliant electrode arrays that aregentle to the walls of the scala tympani, whether the electrode array isintended to engage the medial or lateral wall of the scala tympani.

[0035] It is yet another feature of the invention to provide adifferentially compliant lead having a stiff, substantially straightsection and a more compliant distal, curved section.

[0036] It is a further feature of the invention to provide a lead havinga stylet insertion channel and devices for sealing the opening of thestylet channel.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The above and other aspects, features and advantages of thepresent invention will be more apparent from the following moreparticular description thereof, presented in conjunction with thefollowing drawings wherein:

[0038]FIG. 1 shows, in accordance with the present invention, anillustration of one embodiment of the cochlear lead with an electrodearray having about a 360° spiral curvature for perimodiolar placement;

[0039]FIG. 2 shows, in accordance with the present invention, anillustration of another embodiment of the cochlear lead with anelectrode array that is much longer and less curved and has a tip thatis more tapered and designed for deeper, lateral placement in thecochlea (between about 1.5 to 2.0 turns in the cochlea) compared to thelead of FIG. 1;

[0040]FIG. 3A shows, in accordance with the present invention, across-sectional view of the lead of FIG. 2 at line 3A-3A;

[0041]FIG. 3B shows, in accordance with the present invention, across-sectional view of the lead of FIG. 2 at line 3B-3B;

[0042]FIG. 3C shows, in accordance with the present invention, afragmentary view showing the exposed electrode contacts on the medialside of the lead of FIG. 2;

[0043]FIG. 3D shows, in accordance with the present invention, a partialview of zigzag conductor wires coupled to three electrode contacts;

[0044]FIG. 4 shows a partial, longitudinal, cross-sectional view of oneembodiment of a lead of the present invention, omitting the conductingwires, but showing an integrated Teflon tubing that forms a part of thestylet insertion channel and an overmold that caps the end opening ofthe stylet insertion channel;

[0045]FIG. 5 shows, in accordance with the present invention, anotherlongitudinal, cross-sectional view of the overmold and part of thecochlear lead shown in FIG. 4;

[0046]FIG. 6 is, in accordance with the present invention, across-sectional view of the overmold and the cochlear lead shown in FIG.5 along lines 6A-6A, showing a cross-configured slit in the overmold;

[0047]FIG. 7A shows, in accordance with the present invention, a pinplug that caps an overmold slit opening into a stylet channel and a pinplug insertion tool for holding the pin plug while it is inserted intothe overmold slit;

[0048]FIG. 7B shows, in accordance with the present invention, analternative device for sealing the overmold slit, which device is amalleable, cylindrical ring installed around the overmold slit and whichring can be crushed to compressively seal the overmold slit and hencethe stylet insertion channel;

[0049]FIGS. 8A through 8D depict various views of the manufacturingprocess for assembling the electrode array of the present invention andcoupling the conductor wires to the plurality of electrode contacts;

[0050]FIG. 9A shows a close-up view of a zigzag conductor wire that maybe used in the cochlear electrode of the present invention;

[0051]FIG. 9B shows, in accordance with the present invention, a view ofthe zigzag wire conductor forming apparatus comprised of two wheels (orgears or cylinders) having complementary teeth, which apparatus can beused to quickly manufacture the zigzag conductor wire;

[0052]FIG. 9C shows, in accordance with the present invention, a view ofan in-line electrode array assembly showing the foil strips in a “T”configuration before the foil strips are folded;

[0053]FIG. 9D shows, in accordance with the present invention, anillustration of a heat cured polymer being applied to a surface of afolded leg of the “T” indicated by an “X” and to the top flap of the“T.”

[0054]FIG. 9E shows, in accordance with the present invention, across-sectional view of the electrode assembly of FIG. 9D showing thelayer of polymer over the top surface before the flaps of the top of the“T” are folded over;

[0055]FIG. 10 shows, in accordance with the present invention, a view ofa thin mandrel inserted within the lumen of a Teflon tubing, whichTeflon tubing can be part of the lead shown in FIGS. 4, 5, 7A or 7B;

[0056]FIG. 11 shows, in accordance with the present invention, a view ofa molding apparatus for forming a polymer carrier, e.g., silicone orpolyurethane that covers an electrode array assembly;

[0057]FIG. 12 shows, in accordance with the present invention, anotherview of the curved, electrode assembly and the molding apparatus of FIG.11;

[0058]FIG. 13 shows, in accordance with the present invention, across-sectional view of the mold for forming the carrier/covering overthe electrode array assembly; and

[0059]FIG. 14 shows an apparatus for implanting the electrode array ofthe present invention into a chamber of the cochlea.

[0060] Corresponding reference characters indicate correspondingcomponents throughout the several views of the drawings.

DETAILED DESCRIPTION OF THE INVENTION

[0061] The following description is of the best mode presentlycontemplated for carrying out the invention. This description is not tobe taken in a limiting sense, but is made merely for the purpose ofdescribing the general principles of the invention. The scope of theinvention should be determined with reference to the claims.

[0062] The cochlear electrode of the present invention may be used withan implantable multi-channel pulse generator, e.g., an implantablecochlear stimulator (ICS) of the type disclosed in U.S. Pat. No.5,603,726, incorporated herein by reference in its entirety or withother suitable stimulators. It is to be understood, however, thatalthough a cochlear lead is used as an exemplary context, the lead ofthe present invention, including the method of manufacturing, may beapplied to other medical applications.

[0063]FIG. 1 shows one embodiment of the lead 150 made in accordancewith the present invention. In a cochlear application, the lead 150 hasan outer (lateral) surface 74 for contacting a lateral wall in scalatympani, a medial surface 73 which is opposite the lateral surface 74,and a distal tip 72. The lead has approximately a 360° curvature at thedistally located electrode array 70 and is intended to be implanted inthe cochlea with a turn of between about 360° to 400° (or about one fullturn). The lead is comprised of an electrode array 70 that has aplurality of spaced-apart electrode contacts 200, a middle section 30shown as between point A to point B in FIG. 1, which middle section maybe substantially straight or slightly curved. This middle section 30which is referred to as the “substantially straight section” shallinclude all lead embodiments that are in fact straight, as well as thoseleads which are slightly curved in section 30. It can be seen that thesubstantially straight section 30, can overlap a part of the electrodearray 70 which array also encompasses the distal curved part of the lead71. A thin section 45 of the lead, shown in FIG. 1 as right of point Aon the lead and a thicker, more proximal lead portion 110 carries aplurality of conductor wires 202 for connection to an implantable,multi-channel stimulator or to an ICS which can be inductively poweredthrough the skin. The thin, lead section 45 is thinner than thesubstantially straight or slightly curved section 30 which isnecessarily thicker to accommodate the stylet insertion channel 40. Thedistal curved part 71 of the lead 150, which includes the electrodearray 70, straightens when a stylet is inserted into the stylet channel40. As the stylet is withdrawn, the curved parts of the lead, beingformed from a material having memory, tends to returns to its originalcurved position.

[0064] Some representative dimensions of this lead 150 can be asfollows. The substantially straight section 30 can be about 15millimeters long. This substantially straight section 30 combined withthe curved electrode array portion 70 which partially overlaps, may beabout 25 millimeters long. The width of the electrode array section 70may be about 3.0 millimeters in diameter plus or minus 0.5 millimeters.Proximal lead portion 110 is connected to the thin lead section 45 andmay be variable in length.

[0065] The profile of the lead 150 along its length can vary, as shownin FIG. 1. For example, electrode array 70, in addition to beingaggressively curved, can be gently tapered towards the distal end of thelead 150. Such tapering accommodates the natural, tapered shape of thescala tympani wherein the electrode array 70 is to be inserted. The lead150 has a stylet insertion channel 40 and may have a channel opening 50.The channel 40 extends through the substantially straight section 30 ofthe lead 150 and proceeds further into the aggressively curved part ofthe lead which is part of the electrode array 70.

[0066] The plurality of conductor wires 202 are coupled to the electrodecontacts 200 in the electrode array 70 and these conductor wires extendthrough the lead to the proximal lead portion 110 and may be terminatedin a proximal connector (not shown). The embodiment of the electrodearray 70 shown has sixteen electrode contacts 200, each numbered from #1to #16. Electrode contacts numbered #10 through #16 are within thesubstantially straight (or slightly curved) section 30 of the lead,while the electrode contacts #1 through #9 are within the aggressivelycurved section of the lead.

[0067] The insulative covering/carrier 60 which forms the body of thelead and provides a covering over the conductor wires 202 can be madefrom silicone, polyurethanes or other body-compatible, polymericinsulating materials. The type and hardness of the insulative carrier 60can be selected to provide a specific, desired compliance to the leadbody in combination with the compliance of the conductor wires andchoice of structures incorporated into the lead 150, e.g., the styletinsertion channel 40.

[0068] An important aspect of the present invention which determines thelead's mechanical characteristic is that the carrier/covering materialis molded to assume a specific pre-curved shape having memory.Therefore, the natural resting position of the lead has a curved, distallead tip. When the distal tip is straightened by inserting a relativelystiff stylet into the stylet insertion channel 40, the carrier/covering60 in the distal curved tip as well as the slightly curved section 30 ofthe lead 150 stores elastic energy which exerts a contractive forcetending to restore the lead to its originally molded curved shape. Thelead embodiment in FIG. 1 shows a spiral curve at the tip of the lead,which tip completes a 360° circular loop. When such a lead is implanted,the medial side of the lead having the electrode contacts 200 hugs themodiolar wall and thus achieves a medial electrode array placement.

[0069]FIG. 2 shows an alternative embodiment of a lead 150′, made inaccordance with the present invention, which is similar in constructionto the lead 150 depicted in FIG. 1, except with respect to the degree ofcurvature of the distal portion of the lead and the length of the curvedelectrode array which can be up to two and half times longer for thelead shown in FIG. 2. The lead in FIG. 2 assumes a hooked shaped and hasa curvature which is less aggressive than compared to the lead depictedin FIG. 1. The lead embodiment of FIG. 2 is used for deep, lateralimplantation of the electrode array into the cochlea. The lateral sideof the lead 150′ is that side opposite to where the electrode contacts200 are located.

[0070] The electrode array, when implanted, may turn inside the cochleafrom between about 1.5 to about 2.0 turns. The distal lead tip which haselectrode contacts #1 to #5 is very narrow and tapered. This particulartapered shape accommodates the tight curvature and narrower passagewayproceeding into the duct of the scala tympani, particularly in thesecond turn. In addition, the tapered lead tip containing electrodecontacts #1 to #5 is “super-flexible”, in part, owing to the thinness ofthe tip and, moreover, by selecting an extremely compliant carriermaterial and further by utilizing a compliant, zigzag conductor wire.The overall curvature of the electrode array in FIG. 2 is more gradualthan the one depicted in FIG. 1.

[0071] In use, the electrode array shown in FIG. 2, will tend to abutagainst the outer (lateral) wall in the scala tympani while beinginserted. The contact pressure with lead 150′ is also between the leadand the lateral wall, unlike lead 150, which contacts the medial wall inthe scala tympani. While such lateral lead contact is generally lessefficient for stimulation because it places the electrode contactsfurther away from the target ganglion nerves, this mode of placement anddegree of electrode array curvature may be advantageous when implantingthe electrode array deeply into the cochlea for more than 1.5 turns,since a more aggressive curvature, such as used in the lead 150 shown inFIG. 1, can cause undesirable sticking or jamming in the second turn ofthe cochlea when combined with an increased length to the electrodearray.

[0072] Referring to both FIGS. 1 and 2, the electrode contacts 200 arespaced apart along the medial side of the lead, which side is on theinside of the curvature of the curved electrode array. In the leadembodiments shown, the electrode arrays are positioned as “in-line”electrodes, meaning that they are spaced apart more or less in alignmentwith the lead axis. To have an in-line configuration of electrodes, aperfectly straight alignment is not necessary. Rather, “in-line” shallmean, as used herein, two or more electrodes placed on a linear lead,one electrode placed more distal to another electrode.

[0073]FIG. 3A depicts a cross-sectional view at line 3A-3A of the leadin FIG. 2, showing the insulation coated conductor wires 202 within thetriangular-shaped electrode contact 200. The triangular-shaped electrodecontact 200 is comprised of two folded strips 220 and 210. Theinsulation coated conductor wires 202 may be enclosed in a triangleshape when strip 220 is folded. Alternatively, the strips may be foldedupwards into a “U” shape. Note that there is no stylet channel in thisview since the channel 40 does not extend this far into this distal,super-flexible tip of the lead.

[0074]FIG. 3B shows a cross-sectional view at line 3B-3B of the lead inFIG. 2, showing the stylet insertion channel 40 within thecarrier/covering 60 and the conductor wires 202 within thetriangular-shaped electrode contact 200. The triangular-shaped electrodecontact 200 is comprised of two folded strips 220 and 210. The channel40 may be coated with a slippery material to facilitate the insertionand withdrawal of a stylet. Alternatively, in one preferred embodiment,the insertion channel 40 may be formed from a tube 41 which presents itsown wall, as shown in FIG. 3B.

[0075] As further shown in FIG. 3B, the inside surface of the triangularelectrode 200 may be coated with an insulation coating 205 whichprevents the possibility of shorting through an inadvertent exposure ofthe insulation of a conductor wire 202. The conductor wires 202 areinsulated with a material such as parylene or Teflon® coating. In theevent that the insulation is scraped off from the conductor wire, thepresence of the inner coating 205 can prevent a short to the electrode200. While the cross-sectional view of FIG. 3B is taken with respect toFIG. 2, it will be appreciated that this same view applies equally tocross-sections of the lead in FIG. 1 taken at approximately the samelocations.

[0076]FIG. 3C is a fragmentary, medial view of an electrode array 70 ofthe lead shown in FIG. 2 showing an example inter-contact spacing forthe electrode contacts 200 exposed on the surface of the lead carrier.The electrode contacts 200 can have a surface area having dimensions ofabout 0.50 by 0.40 millimeters and the inter-contact spacing can beabout 1.20 millimeters.

[0077]FIG. 3D shows, in accordance with the present invention, anelectrode array assembly 79 with a view of the conductor wires 202′,202″ and 202′″, which are zigzagged in shape in one embodiment of thelead. The electrode contacts shown are #1, #2 and #3. Zigzaggedconductor wire 202′ is connected to the electrode contact #3 electrodewhile conductor 202″ and 202′″ run past electrode contact #3 through thetriangular electrode assembly. Next, conductor wire 202″ is connected toelectrode contact #2 and conductor wire 202′″ is run through thetriangular electrode assembly of electrode contact #2. Finally, the lastconductor 202′″ is attached to the last and most distal electrodecontact #1. The basic connection sequence shown for electrode contacts#1, #2 and #3 is followed for the remaining electrode contacts # 4through #16 which are not shown in FIG. 3D.

[0078] The zigzagged conductor wires described resist bending fracturesbetter than a straight conductor wire. At the same time, in combinationwith a soft, compliant carrier/covering, the zigzagged wires permit thelead to exhibit higher compliance compared to a lead using otherconductor configurations such as coils or straight conductor wires. Thishigher compliance advantageously allows the curved electrode array 70,as shown in FIG. 2, and particularly the super-flexible tip 260 to bevery compliant while the electrode array is being implanted into thecochlea and, thus, to be very gentle to the cochlear walls. Furthermore,because of this higher compliance, the electrode array does not placeundue pressure on the walls of the cochlea while the array ischronically implanted, thereby averting even the remote possibility ofwall damage after implantation.

[0079]FIG. 4 shows, in accordance with the present invention, oneembodiment of the lead 150 showing a partial, longitudinal,cross-sectional view. This view omits showing the conductor wires andthe proximal end of the lead. The stylet channel 40 is partly formed byplacing a Teflon® (or PTFE) tubing 41 into the slightly curved section30 (between points A and B) of the lead 150. It is emphasized, however,that beyond point B, the stylet channel section 52 is formed by thecarrier material itself, such as silicone or polyurethane since thecurved tip must be flexible and the Teflon would add undesirablestiffness to the tip. The Teflon tubing 41 provides a separate wallwhich is more abrasion and tear resistant than the surrounding materialof the insulative carrier. The Teflon surface also tends to be smootherand presents less friction to an inserted stylet than the insulationcarrier. The stylet channel 40 formed partly by the Teflon tubing 41therefore facilitates the easy insertion of the stylet into the channeland removal when the stylet is no longer needed. A stickier materialsuch as silicone, however, can cause binding between the stylet and thelead and increase the chance for dislodging the lead from its desiredlocation.

[0080] The Teflon tubing 41 provides a second important advantage: itprovides added stiffness to the lead 150 to maintain the substantiallystraight or slightly curved section 30 from buckling during insertion ofthe electrode array section 70 into the cochlea. The tapered, curvedportion of the electrode array which is not stiffened by the Teflontube, however, remains desirably compliant as the insertion stylet isinserted into the stylet channel and as the electrode array is pushedoff the stylet. The substantially straight (or slightly curved) section30 of the lead is advantageously more stiff, since it needs to remainstraight during implantation. Because it does not enter the cochlea, thesubstantially straight section 30 does not need to be as compliant asthe highly curved section of the lead. The Teflon tubing 41 therebyadvantageously provides a differential compliance for the differentsections of the lead 150.

[0081]FIGS. 4 and 5 show, in accordance with the present invention, anovermold 75 which may be used to cover the end opening 50 of the styletinsertion channel 40. It is noted that FIGS. 4 and 5 omit showing theconductor wires for purposes of simplicity. The overmold 75 can be madefrom an implantable grade silicone, polyurethane or other polymermaterial and can have a puncture or a slit 76 therethrough, as shown inFIG. 5. FIG. 5 also shows a Teflon tubing 41 incorporated into the leadin conjunction with the overmold 75. The Teflon tubing 41 can form thestylet channel 40 and the tubing or channel opening 50 can abut theovermold 75 as shown. A tip of an insertion stylet 77 can be insertedthrough the slit 76 and into the stylet insertion channel 40 when theelectrode array is being implanted. After implantation, the stylet 77 iswithdrawn from the insertion channel 40 and the slit 76 in the overmold75, being made of compliant material, will tend to return to itsoriginal state, closing the slit.

[0082]FIG. 6 shows, in accordance with the present invention, across-sectional view of the overmold and part of the lead at line 6A-6Aof FIG. 5. For simplicity, the conductor wires running through the leadare not shown in FIG. 6. While a cross-configured slit 76 is depictedhere, it can be appreciated that other configurations of punctures orslits can be used with equal effect.

[0083] The slitted overmold 75 helps to keep unwanted bacteria fromentering the stylet channel after the lead/electrode array has beenimplanted. If the stylet channel opening 50 is not covered, there is anincreased chance that the stylet insertion channel 40 may become a sitefor bacterial growth, particularly since the open stylet channel mayeasily allow entry of bacteria but cannot be reached by the body'scellular, immune defense, i.e., white cells. There is a remotepossibility that bacteria that has grown in the stylet channel willescape into the cochlea through small pores or fissures in the wall ofthe carrier/covering. The use of an overmold to seal the opening of thestylet channel can help forestall this occurrence.

[0084]FIG. 7A-C illustrate, in accordance with the present invention,two devices that may be used to further cap the slitted overmold shownin FIG. 5 after the insertion stylet has been removed. FIG. 7A shows apin plug 95 having a circular head 93 and a tail pin 94 having acurvature 90 in the middle of the pin. To help insert the pin plug 95into the overmold 75, a pin plug insertion tool 97 may be used. Theelongate insertion tool 97 has a first end 98 and a second end 99 andhas a small channel 92 on the first end 98. The tail pin 94 of the pinplug 95 can be inserted into the small channel 92 which has a diameterthat is sized to accept the tail pin and hold it tightly in afriction/compression fit. The exterior diameter of the first end of theinsertion tool 97 may be about the same diameter or smaller than the pinplug head 93. As such, the pin plug head 93 and the first end 98 of theinsertion tool 97 may be inserted head first through the cross slit 76shown in FIG. 6 and inserted into the compliant overmold 75 such thatthe pin plug head 93 is abutted against the tubing end 51 to help sealthe channel 40. As the insertion tool 97 is withdrawn from the overmold75, the pin plug 95, which is compressed and grabbed by the compliantovermold 75, will remain in place within the overmold. The tail 94 maybe left protruding from the overmold 75 without concern. This tail 94may be grasped at some later time to retract the pin plug 95 from theovermold 75, if necessary.

[0085]FIG. 7A also depicts an embodiment of the lead in which a Teflontubing 41 forms the stylet channel 40. In such a case an overmold 75 mayalso be employed. The Teflon tubing end 51 is placed abutted to theovermold 75. The thickness of the overmold may be, for instance, about1.0 millimeter. As other example dimensions, the stylet channel 40 canhave an inner diameter of 0.30 millimeters and the diameter of the pinplug head 93 can be 0.40 millimeters. The pin plug 95 can be made of, inone embodiment, body compatible polymer or non-corroding metals such asplatinum, platinum/iridium alloy or gold or a combination thereof.

[0086] As shown in FIG. 7B, another method for capping the tubing end 51is to employ a small, malleable, ring 43 implanted at the opening of thestylet channel 40. A Teflon tubing 41 may be used to form the styletinsertion channel 40. There is no separate overmold in the example leadshown in FIG. 7B. The ring 43 may be made of a body compatible,malleable metal. The slit 76 in the carrier insulation can be closed bycrushing the ring 43 around the slit.

[0087]FIGS. 8A through 8D illustrate one method of making the electrodearray assembly 79 of the present invention. To illustrate the process ofassembling the electrode contacts and the conductive wires, the processwill be described relative to the fabrication of an electrode arraysuitable for insertion into the cochlea. It should be emphasized thatthe method of making the electrode array depicted in these figures isnot the only way to make lead 150 and electrode array 70. However, itrepresents one way to easily and inexpensively make the leads andelectrode arrays depicted in FIGS. 1 and 2.

[0088] Most designs of cochlear leads and connectors are made by forminga polymer carrier such as silicone or polyurethane over an assembly ofelectrode contacts 200. The electrode contacts 200 which actually makecontact with the stimulated tissue are generally made from abiocompatible, electrically conductive material such as an electricallyconductive, relatively inert metal, e.g., platinum or a platinum/iridiumalloy. The electrode contacts 200 are located in a controlled positionin reference to the surface of the lead carrier, with a specifiedsurface portion of the electrode contact left exposed for contacting thebody tissue to be stimulated. Disadvantageously, making such electrodearrays can be extremely difficult, especially when the electrodecontacts are very small and when a large number of electrode contactsare used, as is the case with a cochlear lead. One problem encounteredin the fabrication of such electrodes is reliably holding the array ofelectrode contacts in the desired and stable position when welding theconductive wires to the contacts and when molding the carrier over theconductive wires. A further problem is to ensure that the portion of theelectrode contact surface which is to be exposed is not covered by thecarrier when the lead is molded.

[0089] As provided in FIGS. 8A through 8D, one method of making theelectrode array of the present invention employs the principle ofattaching electrode contacts 200 onto a chemically dissolvable,non-toxic, foil substrate 100, such as iron (Fe). The electrode contacts200 can be made from precious, relatively non-reactive materials, e.g.,platinum and its alloys, such as platinum/iridium. The electrodecontacts can be resistance welded to the foil substrate 100. Resistancewelding advantageously provides a secure attachment of the electrodecontact material to the foil substrate 100 without causing a deep fusionattachment of the two materials. The resulting shallow fusion yields aclean, exposed electrode surface area to be formed when the foil carrieris later chemically etched away. Other types of attachment that resultin shallow fusion between the electrode material and the foil substratemay be used in lieu of resistance welding.

[0090] Attached to the metal foil substrate 100, the electrode contacts200 remain in a desired and stable position allowing the conductor wires202 to be easily connected to the contacts 200 and, subsequently,allowing the insulative polymer carrier to be molded over the conductorwires 202. After the molding process is completed, the metal foil ischemically etched away using a mixture of diluted acids, such as HNO₃ orHCl, heated to 90° Celsius. The electrode contacts and polymer carrierare largely inert to the acid and hence remain unaffected.

[0091]FIG. 8A illustrates an electrode array assembly 79 comprised ofelectrode contacts 200 which are resistance welded onto an Fe substrate100 assuming an in-line, spaced-apart configuration. One conductor wire202 can be uniquely coupled to the electrode contacts 200 that arenumbered # 1-16. For simplicity, only six of the sixteen electrodecontacts used in the electrode array 70 are shown in FIG. 8A. Typically,a conductor wire 202 will connect to one of the electrode contacts 200and another conductor wire from bundle 203 will connect to anotherelectrode contact 200 and so on.

[0092]FIG. 8B shows that each electrode contact 200 consists of twopieces of platinum strips 210 and 220 connected together and joined tothe iron foil 100 (FIG. 8A) by a shallow-fusion spot weld. These stripsare initially arranged to form a “T” shape, viewed from the top, withthe strip 210 forming the leg of the “T” and the strip 220 forming thecross bar of the “T”. The legs of each “T” are arranged in-line, withproper spacing therebetween.

[0093] As seen in FIG. 8B, an insulated conductor wire 202′ is laid ontop of the electrode foil strip 220. The leg of the “T”, which is thefoil strip 210, is then folded over to hold the end of the conductorwire 202′ while it is welded in position. The weld, preferably aresistance weld, burns away any insulation from the tip of the conductorwire 202′ and makes a secure mechanical and electrical connectionbetween the wire 202′ and the electrode contact 200.

[0094]FIG. 8C shows the result of an electrode contact 200 having a wire202′ securely attached thereto. If other conductor wires are present,e.g., going to more distal electrode contacts, then such wires can passover the foil piece 210 to form a bundle of conductor wires. The endflaps of the strip 220 may then be folded upwards to form, in a oneembodiment, a triangular shape, as depicted in FIG. 8D. Alternatively,the end flaps of the strip 220 may be folded into an open “U” or stapleshape, instead of a triangular shape.

[0095] While FIGS. 8A-D show zigzagged wire conductors 202, straightconductors may be used for some cochlear applications. Nevertheless,when high lead compliance is desired, a zigzag conductor wire 202 shownpreviously in FIG. 3D, is preferable. The method of assembling theconductor wires and coupling them to the electrode contacts 200,however, is essentially identical to the process described above forFIGS. 8A-D whether the conductor wires are zigzagged or straight.

[0096]FIG. 9A depicts, in accordance with the present invention, onestrand of a zigzag conductor wire 202 showing one set of conductor wiredimensions used in a cochlear stimulation lead. The conductor wire 202can have a diameter of about 0.025 millimeters, a trough-to-peak widthof 0.20 millimeters and, R, the radius of curvature 56 of a peak (or atrough) of 0.05 millimeters, and a single bend of approximately 90°between adjacent wire segments 57 and 58.

[0097]FIG. 9B illustrates, in accordance with the present invention, anapparatus 85 used for manufacturing a zigzag conductor 202 wherein twotoothed wheels (or cylinders) 80 and 81, respectively, are employed. Thefirst wheel 80 has teeth 82 and the second wheel (or cylinder) 81 hascomplementary teeth 83. It can be seen that the teeth 82 andcomplementary teeth 83 can be shaped in many configurations, includingthat which yields the zigzag wire shape shown in FIG. 9A. One strand ofstraight wire 204 may be fed into the rotating wheel apparatus 85 toproduce one strand of zigzagged conductor wire 202. Alternatively,multiple strands of straight conductor wire 204 may be drawn between thetwo rotating wheels simultaneously to manufacture multiple strands ofzigzagged conductors 202. The first wheel 80 and second wheel 81 areplaced in a zigzag wire forming apparatus with a clearance between thetwo wheels to bend straight wire into zigzag wire. The clearance shouldbe sufficient to allow the conductor wire or wires to pass withoutbecoming crushed and pinched while forming the zigzag wire shape.

[0098]FIG. 9C shows a close-up view of how one strand of zigzaggedconductor wire 202 is connected to electrode contact #16. Another wirestrand is coupled to electrode contact #15 and so on until the last wirestrand is connected to electrode contact #1. Then, the two flaps ofstrip 220 are folded upwards into a U shape or an enclosing triangle,while the bundles of conductor wires 202 are within the space betweenthe flaps.

[0099]FIGS. 9D and 9E illustrate, in accordance with the presentinvention, a preferred embodiment for manufacturing the electrode arrayby placing an insulation covering on the inside of the triangular-shapedelectrode contact. After a conductor wire 202 has been welded to theelectrode contact, a coating of insulation 205 is applied to the insidesurface of foil 210 of the electrode contact 200 to provide aprecautionary insulative barrier in the unlikely event that one of thepassing wire conductors 202 should have an inadvertent exposure in theinsulation covering. While there are many types of insulation materialthat may be applied, a preferred material is a polymer 205, as shown inFIG. 9D, that may be quickly cured with an application of heat and watervapor. Alternatively, the polymer 205 may be cured by applying a dose ofultraviolet radiation to a UV sensitive polymer.

[0100]FIG. 10 shows, in accordance with the present invention, a smalldiameter, Teflon mandrel 42 inserted into a thin-walled, Teflon tubing41. This mandrel 42 is employed to make a lead which has a Teflon tubing41 forming the stylet insertion channel 40, as shown in FIG. 4. Duringmolding of the carrier/covering 60 of lead 150, the mandrel 42 isinserted into the channel of tubing 41. After the carrier/covering ismolded over the completed electrode assembly with the conductor wiresconnected, the mandrel 42 is withdrawn leaving the Teflon tubing 41inside the lead carrier/covering and forming a stylet channel 40 withinthe lead.

[0101]FIGS. 11 and 12 show, in accordance with the present invention, adie and rod apparatus for molding the carrier over the conductive wires202 and electrode contacts 200 that are pre-welded to an Fe substrate100. One end 108 of the Fe substrate is fixed to a revolving dowel 104which can be rotated to curve the Fe substrate and electrode arrayassembly 103. To create a lead shown in FIG. 1, the dowel 104 is rotated360° to create the circular loop, as shown in FIG. 12. The other end 109of the Fe substrate 100 is fixed to an attachment and restraint device102 which keeps the substrate under continuous tension while the dowel104 is rotated. After the circular loop is created at the distal part ofthe electrode array assembly, silicone is injected into the cavity 115of the mold 105 which can be comprised of at least two detachable pieces106 and 107.

[0102]FIG. 13 shows, in accordance with the present invention, across-sectional view of the die and electrode as shown in line 13A-13Aof FIG. 11. In the first molding pass the U-shaped, carrier portion 108is created by placing a first complementary die (not shown) over the topof the open die portions 107 and 106 and injecting a carrier polymerinto the formed cavity 115, which cavity is shaped as the exterior ofcurved section of the lead. In the second molding pass, the firstcomplementary die is removed and a Teflon mandrel 42 is inserted intothe U-shaped trough 117. A second complementary die (not shown) isplaced over the open die portions 106 and 107 and then silicone isinjected into the remaining formed cavity and carrier portion 109 isformed which melds seamlessly with carrier portion 108. All diesections, including the second complementary die and die pieces 106 and107, are disassembled and the lead assembly with the formedcarrier/covering is freed from the mold. Then, the mandrel 42 is pulledout through stylet channel opening 50 creating the stylet channel 40. Aseparate overmold may be attached over the stylet channel opening 50. Atsome point after the lead has been released from the mold, weak heatedacid is applied to dissolve the Fe substrate 100, which is no longerneeded to hold the electrode contacts 200, thereby exposing theelectrode contacts 200 on the surface of the lead.

[0103] If a Teflon tubing is desired as part of the stylet insertionchannel, the combination of the Teflon tubing 41 with a Teflon mandrel42 inserted within the tubing 41 is used, as shown in FIG. 10. Thiscombination is then implanted into the trough 117 of carrier 108 insteadof the Teflon mandrel 42 alone. The Teflon tubing should be positionedin the die 106 and 107 so that it is placed in the substantiallystraight or slightly curved portion 30 of the lead 150 or 150′ suchthat, after being molded into the carrier, the Teflon tubing 41 willcontribute to lead insertion stiffness and provide a slippery channel 40for the insertion stylet. After the carrier/covering 108 and 109 aremolded over the electrode/conductor wire assembly 103, the Teflonmandrel 42 is withdrawn, leaving the Teflon tubing 41 intact within thelead 150 or 150′, and which Teflon tubing forms the stylet insertionchannel 40.

[0104]FIG. 14 shows an apparatus 500 for gently implanting a pre-curvedcochlear electrode array 70 as exemplified in FIGS. 1 and 2. To use thisimplanting apparatus 500 the lead must have a stylet insertion channel40 since the apparatus 500 employs an insertion stylet 400 with arounded tip 410. As noted previously, inserting the stylet 400straightens a pre-curved lead 150 or 150′ so that it may be initiallyinserted into the scala tympani 420. After the distal end of the arm 430is abutted against the bone 450, the implanting apparatus 500 uses thestylet 400 as a guide and the sleeved part 434 is pushed using handle431. A handle 431 is attached via arm 432 which is, in turn, connectedto the sleeved part 434. The lead 150 is pushed off the stylet and, atthe same time, the distal lead tip 152 is gently pushed into thecurvature of the scala tympani 420, while the insertion stylet ismaintained in a fixed position. The electrode array 70 of the lead 150is radially oriented during insertion relative to the cochlea so thatthe electrode array 70 of the lead 150 can return to its original moldedcurvature within the scala tympani. Because of this tendency to returnto the original curved shape, the tip 152 of the lead will follow aspiral pathway as the electrode array 70 is gently pushed off the styletand into the cochlea.

[0105] The insertion apparatus arm 430 abuts against bone 450 hencelimiting the depth of initial insertion of the electrode array andstylet tip 410 into the cochlea and thereby avoiding possible injury tothe wall of the scala tympani. It can be seen with this particularimplantation method that insertion and retraction of the stylet can begreatly facilitated by employing an insertion channel formed by anintegrated Teflon tubing, since such a channel will exhibit superiorabrasion resistance and low friction. In addition, the added stiffnessprovided by the Teflon tubing facilitates the initial placement of thelead 150 or 150′ at the entrance of the scala tympani 420.

[0106] The lead design disclosed in FIG. 1 is a perimodiolar design formedial contact and which lead design has a curvature that places theelectrode array near the modiolar wall. Thus, cells embedded within themodiolar wall may be stimulated at a lower energy setting than would berequired if the electrode contacts were not facing the modiolar wall.Such an electrode array placement achieves the desired stimulation atthe lowest possible power levels. The electrode design of the presentinvention, however, is adaptable and, as shown in FIG. 2, can be madewith an electrode array with a wider arc. The electrode array of FIG. 2,which is used to deeply insert the electrode array between about 1.5 and2.0 turns in the cochlea, will tend to uncurl with greater pressureapplied between the lead and lateral wall of the scala tympani. A widerarc for the curvature is better suited to an electrode array which isvery long, and this particular embodiment has a very thin andsuper-flexible tip optimal for deep, lateral placement, because such awider arc can prevent jamming or sticking while the electrode array isbeing inserted into the cochlea. In either embodiment of the lead of thepresent invention, the lead can be placed into the cochlea very gentlyto avoid damage to the cochlear walls. It is thus seen that a lead isprovided that has enhanced performance and that is easily assembled.

[0107] While the invention herein disclosed has been described by meansof specific embodiments and applications thereof, numerous modificationsand variations could be made thereto by those skilled in the art withoutdeparting from the scope of the invention set forth in the claims.

What is claimed is:
 1. An implantable lead for use with electricalstimulation, the lead comprising: a flexible carrier having a proximalend, a distal end, a medial side and a lateral side; a distal,pre-curved lead section having memory; a plurality of electrode contactsembedded at the distal end of the lead, which electrode contactscomprise an electrode array; a plurality of conductor wires embedded inthe carrier, each conductor wire connected to at least one electrodecontact; and a longitudinal stylet insertion channel in the carrierextending into at least a part of the distal, pre-curved lead section.2. The lead of claim 1, wherein the electrode contacts and connectedconductor wires are pre-bent to a desired pre-curvature before theflexible carrier is molded over the electrode contacts and conductorwires.
 3. The lead of claim 1, wherein the distal, pre-curved leadsection is dimensionally pre-curved to conform to about one spiral turnin a human cochlear duct; and wherein the distal, pre-curved leadsection has a curvature, taper and size to provide medial contact withthe cochlear duct.
 4. The lead of claim 1, wherein the lead has a distalpart that is substantially hooked shaped and has a spiral curvaturedimensioned to conform to a human cochlear duct and also to providelateral contact with this cochlear duct; and wherein the distal,pre-curved lead section is dimensionally tapered and sized so that theelectrode array can be implanted to exceed about 1 turn inside thecochlear duct.
 5. The lead of claim 4, wherein the distal lead isdimensionally tapered and sized so that the lead can be implanted nogreater than about 2 turns inside the cochlear duct, which duct is thescala tympani.
 6. The lead of claim 4, wherein the most distal tip ofthe lead that includes a subset of the electrode array is constructed asa super-flexible tip; and wherein the super-flexible tip does notinclude the stylet insertion channel and which super-flexible tip has asubstantially smaller thickness than the remainder of the distal leadcontaining the electrode array that is not super-flexible.
 7. The leadof claim 1, wherein the conductor wires are zigzagged conductor wires.8. The lead of claim 1, further comprising an overmold which caps theopening of the stylet channel and wherein the overmold has a slitopening.
 9. The lead of claim 8, wherein the overmold has across-configured slit for allowing an insertion stylet to be insertedinto the stylet insertion channel.
 10. The lead of claim 8, furthercomprising: a pin plug which has a head and a curved tail pin, which pinplug is dimensioned and configured to permit the pin plug to be insertedhead first into the overmold slit opening to seal the slit opening. 11.The lead of claim 8, further comprising: a malleable ring in the leadcarrier encircling the slit in the overmold, which malleable ring can becrushed around the slit to provide a compressive seal to the slit. 12.The lead of claim 1, wherein at least part of the stylet insertionchannel is formed by incorporating a tube into the lead, wherein thetube is made from a different material than the carrier.
 13. The lead ofclaim 12, wherein the tube is a Teflon (PTFE) tube.
 14. A method ofmanufacturing an implantable stimulating lead comprising: (a) attachinga plurality of inert electrode contacts onto chemically dissolvablestrip substrate having a first, distal end and a second, proximal end;(b) coupling each electrode contact to a conductor wire to create anelectrode array assembly; (c) attaching the first, distal end ofsubstrate to a revolving dowel, which dowel is integrated into a moldhaving a cavity, the dowel placed inside the cavity; (d) attaching theproximal, second end of the substrate to a restraint which appliestension to the electrode array assembly; (e) turning the dowel to createa predetermined curvature on the distal end of the electrode arrayassembly; (f) delivering a body-compatible carrier material into thecavity and around the electrode array assembly to create acarrier/covering; (g) releasing the formed lead from the mold; and (h)applying a weak acid and heat to the chemically active substrate todissolve away the substrate and expose the inert, electrode contact onthe surface of the lead.
 15. The method of claim 14, further comprising:between the step (e) and (f), (e1) placing a mandrel into the cavity,oriented approximately parallel to the electrode array assembly, whereinone end of the mandrel is situated to escape coverage by injectedcarrier material; and and after the step (g), (g1) pulling the mandrelout of the carrier to create a stylet insertion channel with a channelopening on the lead.
 16. The method of claim 15, further comprising thestep: (i) attaching an overmold over the opening of the stylet insertionchannel, which overmold has a slit opening.
 17. The method of claim 14,further comprising: between the step (e) and (f), (e1) placing a mandrelinside the lumen of a thin-walled Teflon tubing; (e2) placing thecombination of the Teflon tubing with the inserted mandrel inside thetubing into the mold cavity, the combination oriented approximatelyparallel to the electrode array assembly, wherein one end of the mandrelis situated to escape coverage by the delivered carrier material; andand after the step (g), (g1) pulling the mandrel out of the Teflontubing to create the stylet insertion channel.
 18. The method of claim17, wherein the mandrel is made of Teflon.
 19. The method of claim 17,further comprising the step: (i) attaching an overmold over an openingof the stylet insertion channel, which overmold has a slit opening. 20.A method of implanting an implantable stimulation lead having aninsertion stylet channel with a channel opening on the lead body, themethod comprising: (a) implanting the lead using the stylet; (b)withdrawing the stylet from the lead; and (c) capping the insertionstylet channel opening.
 21. The method of claim 20, wherein capping thechannel opening is accomplished by taking a pin plug, having a head andcurved pin, and inserting the head of the pin plug into the lead to sealthe channel opening.
 22. The method of claim 20, wherein capping thechannel opening is accomplished by providing a malleable ring in thelead body which encircles the channel opening and crushing the ring toseal the channel opening.
 23. A cochlear lead system comprising: acochlear lead including: a flexible carrier having a proximal end anddistal end; a stylet insertion channel incorporated into the flexiblecarrier; and an electrode array placed on the distal lead end; a pinplug for capping the insertion stylet, the pin plug having a head andtail pin with a curvature in the tail pin; and an insertion tool whichhas a first end and second end, wherein the first end has a pin plugholding channel that accommodates the tail pin and holds it within theholding channel with a friction fit.